Magnetic core structures

ABSTRACT

Laminated magnetic cores having leg and yoke laminations which are joined together to form lamination joints. The joints include one or more convex points at one end of a leg lamination and one or more convex or concave points at the other end of the leg lamination. The points are formed by straight portions of the joint which intersect with each other either perpendicularly, acutely or obtusely. The points at different ends of the leg lamination may or may not be aligned with each other. Distribution throughout the core may be achieved by a butted-lap arrangement or by a stepped-lap arrangement, either horizontally, vertically or angularly.

United States Patent Gumpper et al.

3,743,991 July 3,1973

[541 MAGNETIC CORE STRUCTURES FOREIGN PATENTS OR APPLICATIONS 1lnvemorsi John Gumpper, Jamestown; 663.188 5/1963 Canada 336/217 AngeloA. DeLaurentis, Sharpsville, 7 both of Primary Examiner-Thomas J. Kozma[73] Assignee: Westinghouse Electric Corporation, rwrn y S tOfl and F.E. Browder Pittsburgh, Pa. 221 Filed: Aug. 18, 1971 1 ABSTRACT [2]]App]. NO: 172 849 Laminated magnetic cores having leg and yokelaminations which are joined together to form lamination joints. Thejoints include one or more convex points at [52] US. Cl. 336/217 one endfa leg lamination and one or more convex or [5 Int. Clconcave points atthe other end of the leg lamination [58] Field of Search 336/216, 217The points are formed by straight portions of the joint which intersectwith each other either perpendicularly, References Cited acutely orobtusely. The points at different ends of the UNITED STATES PATENTS leglamination may or may not be aligned with each 3 504 31s 3/1970 Wilburn6! al 336/217 x Other- Distribuion throughm the core may be 1:406:2452/1922 Thordarson achieved y a butted-lap arrangement or y a Stepped-3,153,2l5 10/1964 Burkhardt et al lap arrangement, either horizontally,vertically or angu- 3,214,718 10/1965 Graham larly.

577,480 2/1897 Gutmann 336/217 X 3,210,708 10/1965 Franklin et al.336/217 31 Clams, 15 Drawing Flgures 7 \go 52 h 4 v v k V "L I 54 52PATENTEDJUL 3 B73 S'EHEN'4 FIG. IO.

A w m F FIG. l2.

1 MAGNETIC CORE STRUCTURES BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates, in general, to magnetic corestructures and, more specifically, to laminated magnetic core structurescomprising a plurality of metallic laminations.

2. Description of the Prior Art There are several sources of losses inpolyphase transformer cores in addition to the electrical steelorientation, the lamination stacking arrangement, and the air gapbetween the laminations. The joint regions where the flux from differentlegs meet, the yoke crowding effect, and the rotational flux factor atthe middle leg joints all contribute adversely to the performance of themagnetic core.

Considerable research is currently being applied to the problem ofproducing a high performance polyphase laminated magnetic core. Theproblem is compounded by the necessity of weighing manufacturing andenvironmental considerations against the electrical performance of thecore. The ease with which the laminations may be stacked, the amount ofmagnetic material required to fabricate the core, and the sound levelproduced by an energized core are a few of the considerations which mustbe weighed in determining the optimum arrangement for a magnetic core.While some cores are superior in several of these categories, few if anyexhibit substantially all of the desirable features.

Of the many magnetic cores developed over the years, certain types havebeen standardized for particular applications. Although most of thesecores perform extremely well, certain inherent limitations exist in someof the cores and are considered undesirable. The amount of scrapproduced in punching or shearing the laminations directly affects theeconomic aspects of the magnetic core. The flux patterns dictated by thesize and shape of the lamination joints affect the electricalperformance of the magnetic core. The sound level produced by themagnetic core may determine the feasibility of using a corecommercially. Unfortunately, many conventional arrangements that aresuggested for improving laminated magnetic cores do not provide theimprovements without creating an offsetting disadvantage in otherfeatures of the core.

It would be desirable, and it is an object of this invention, to providea magnetic core which may be fabricated from less material than presentstate of the art cores. It is a further object of this invention toprovide a magnetic core which exhibits better electrical characteristicsat a reduced sound level than present cores. Finally, it is an object ofthis invention to provide a magnetic core which exhibits all of theseadvantageous features.

SUMMARY OF THE INVENTION This invention discloses new and improvedarrangements for constructing a laminated magnetic core. Novelarrangements are provided for the middle leg lamination geometry toimprove the joint between the middle leg and the yoke laminations.

One embodiment discloses middle leg geometry having convex points at oneend and concave points at the other end. Another embodiment disclosesmiddle leg geometry having convex points at both ends with thepossibility of offsetting these points.

Various arrangements may be used to define the points. They may bedefined by straight portions of the joint which intersectperpendicularly, acutely or obtusely. Distribution throughout the coremay be achieved by a butted-lap arrangement or by a steppedlaparrangement, either horizontally, vertically or angularly.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of thisinvention will become more apparent when considered in view of thefollowing detailed description and drawings, in which:

FIG. 1 is a plan view of a layer of laminations according to the priorart;

FIG. 2 is a plan view of a laminated magnetic core constructed accordingto the prior art;

FIG. 3 is a plan view of a layer of laminations according to theteachings of this invention illustrating multiple point middle leglamination geometry;

FIG. 4 is a plan view of a laminated magnetic core constructed accordingto the teachings of this invention illustrating a butted-lap jointdistribution arrangement of the layer shown in FIG. 3;

FIG. 5 is a partial plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating a middle leglamination having a concave and a convex point;

FIG. 6 is a partial plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating a middle leglamination having a plurality of concave and convex points;

FIG. 7 is a plan view of a layer of laminations according to theteachings of this invention illustrating offset point middle leggeometry;

FIG. 8 is a plan view of a laminated magnetic core constructed accordingto the teachings of this invention illustrating a butted-lap jointdistribution arrangement of the layers shown in FIG. 7;

FIG. 9 is a partial plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating a middle leglamination having points formed by straight joint portions which are 60and 30 skew to the sides of the lamination;

FIG. 10 is a plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating verticalstepped-lap distribution of a middle leg lamination having two concavepoints and two convex points;

FIG. 10a is a sectional view of the lamination joints taken along lineX-X shown in FIG. 10;

FIG. 11 is a partial plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating verticalstepped-lap distribution of a middle leg lamination having convex pointsat each end;

FIG. 12 is a partial plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating horizontalstepped-lap distribution of a middle leg lamination having convex offsetpoints;

FIG. 13 is a partial plan view ofa laminated magnetic core constructedaccording to the teachings of this invention illustrating one form ofangular stepped-lap distribution; and

FIG. 14 is a partial plan view of a laminated magnetic core constructedaccording to the teachings of this invention illustrating another formof angular stepped-lap distribution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the followingdescription similar reference characters refer to similar members in allfigures of the drawings.

Referring now to the drawings, and FIG. 1 in particular, there is showna layer of laminations assembled to define a magnetic path having threelegs and two windows. This arrangement is used extensively in electricalinductive apparatus at the present time. The layer of laminations 10includes the outer leg laminations 12 and 14, the middle leg laminationl6, and the yoke laminations 18 and 20. The laminations 16 and 18 arejoined by a butt joint 22 which penetrates the yoke laminations 18 toits longitudinal centerline. The laminations 16 and are joined by abuttjoint 24 which penetrates the yoke lamination 20 to its longitudinalcenterline.

A complete laminated magnetic core 26 constructed according to the priorart is illustrated in FIG. 2. The magnetic core 26 comprises a pluralityof layers of laminations which are identical to the layer illustrated inFIG. 1. Alternate layers of laminations in the core 26 are effectivelyrotated about the axis 28 which is shown in FIG. 1, thus permitting thelaminations in alternate layers to lap the adjacent butt joints. Thisarrangement provides a butted-lap laminated magnetic core having theouter legs 30 and 32, the middle leg 34, and the yoke portions 36 and38.

Because of the geometry of the laminations which comprise the magneticcore 26, voids are produced at the inside corners near the jointsconnecting the middle leg 34 and the yokes 36 and 38. These joints causethe flux which circulates between the outer legs 30 and 32 to occupy theouter region of the yokes. The flux crowding effect in this regionreduces the efficiency of the magnetic core.

An embodiment of this invention which eliminates the voids at the insidecorners and reduces the flux crowding effect is illustrated in FIGS. 3and 4. The layer of laminations 40 shown in FIG. 3 includes the outerleg laminations 42 and 44, the middle leg lamination 46, and the yokelaminations 48 and 50. The butt joint 52 connects the yoke lamination 48to the middle leg lamination 46 and the butt joint 54 connects the yokelamination 50 to the middle leg lamination 46. The joints 52 and 54 havegeometry which allows them to have the same joint length withoutpenetrating the yoke laminations as much as the joint arrangement shownin FIGS. 1 and 2. Thus, the flux crowding effect is reduced by thisarrangement without sacrificing the length of the butt joint. The insidecorners near the middle leg-yoke joint are voidless.

In both the joints 52 and 54, the angles which are formed at the pointsof the joints are right angles. The portion of the lamination 46 whichforms the butt joint 52 is automatically formed by the punchingoperation used in fabricating the lamination 46. A strip of magneticmaterial is indexed into the punching die where a lamination 46 ispunched out, leaving the end of the strip with the geometry shown.Indexing the strip to punch the next lamination produces anotherlamination 46. Thus, the geometry of the lamination 46 permits it to befabricated without producing any scrap material.

The laminated magnetic core 58 which is shown in FIG. 4 is constructedby stacking layers of laminations with the edges of the layers inalignment. The layers are similar to the layer 40 illustrated in FIG. 3with alternate layers rotated around the axis 56. The resulting magneticcore 58 is of the butted-lap type and includes the outer legs 60 and 62,the middle leg 64, and the yokes 66 and 68. The joint 52 is adjacent tothe joint 54', where the prime mark denotes the joint in an invertedlayer of laminations. Similarly, the joint 54 is adjacent to the joint52'. These joints, which are in adjacent layers, are effectivelyperpendicular to each other where they cross. The adjacent joints crossat approximately the middle of the 45 mitered portions of the joints.

The laminated magnetic core 58 which is provided by this laminationstacking arrangement is voidless, has low flux crowding effects and maybe fabricated without any middle leg punching scrap. Scrap loss for theentire core, due mainly to the middle leg scrap savings, isapproximately l.9 percent of the core material required for a 45 KVAtransformer. This is very favorable as compared to the 7.3 percent lossfor a similarly rated core constructed according to the prior art.

Although the outer leg-yoke joints have been specifically illustrated inFIG. 4, the laminations may be punched with other corner joint shapeswithout departing from the teachings of the invention. For instance, thecorner joints illustrated in FIG. 2 may be used. Similarly, it is withinthe contemplation of this invention that the number of points defined bythe geometry of the middle leg lamination may be different than thatshown in FIG. 4.

A point is formed by the mitered portion of the joint. A point is convexwhen it is formed by mitered portions which form an acute included anglewith a lamination side. A point is concave when it is formed by miteredportions which form an obtuse included angle with a lamination side.Thus, the joint 52 includes the convex points 78 and 80 and the joint 54includes the concave points 82 and 84. The convex points 78 and 80 andthe concave points 82 and 84 are formed by mitered portions of thejoints which are perpendicular to each other. Therefore, they arereferred to as right angle convex and right angle concave points,respectively.

A core having a middle leg lamination which includes one right angleconvex point 84 at one end and one right angle concave point 86 at theother end is partially illustrated in FIG. 5. Alternate layers oflaminations are rotated so that the adjacent mitered portions of themiddle leg-yoke joints properly cross each other.

The angles which are' formed by the mitered portions of the joints mayalso be other than right angles. A core having a mitered middle leglamination which includes convex points 88, 90, 92 and 94 at one end andconcave points 96, 98, and 102 at the other end, is partiallyillustrated in FIG. 6. Since the mitered portions of the jointsintersect each other to form angles which are less then right angles,the convex points 88, 90, 92 and 94 are referred to as acute angleconvex points. Similarly, the points 96, 98, 100 and 102 are referred toas acute angle concave points. Other embodiments of the invention mayinclude more or less points and/or obtuse angle points.

A layer of laminations 104 which includes a middle leg lamination withoffset convex points is illustrated in FIG. 7. The layer 104 comprisesthe outer leg laminations 106 and 108, the middle leg lamination 110,and the yoke laminations 112 and 114. One end of the lamination 110 hasgeometry which produces a joint having right angle convex points 116 and118. The other end of the lamination 110 has geometry which producesright angle convex points 120 and 122. Respective points at each end ofthe lamination are offset so that the location of each point is at adifferent predetermined distance from the lamination axis 124.

A laminated magnetic core 126 having middle leg laminations whichinclude offset right angle points is illustrated in FIG. 8. The core 126is constructed by stacking layers of laminations with the edges of thelayers in alignment. The layers comprising the magnetic core 126 aresimilar to the layer 104 shown in FIG. 7 with alternate layers rotatedaround the axis 128. The laminations comprising the core 126 define theouter legs 130 and 132, the middle leg 134, and the yokes 136 and 138.The outer corner joints 140, 142, 144 and 146 connect the yokelaminations to the other leg laminations. Other corner jointarrangements may be used, such as those illustrated in FIG. 2. Themiddle leg joints 115 and 117', which are in adjacent layers, cross eachother perpendicularly. The middle leg joints 115' and 117 similarlycross each other. The joint points in adjacent layers are not adjacentdue to the offsetting geometry of the middle leg laminations.

The unique geometry of the middle leg laminations enables the middle leglaminations to be fabricated without producing any material scrap. Thisfeature greatly improves the percentage of scrap produced in fabricatingthe laminations for the magnetic core 126 over conventional cores. For45 KVA transformers, there is a material savings of 3.6 percent with themagnetic core 126 compared to the magnetic core 26 illustrated in FIG.2. In addition, the flux crowding in the yokes 136 and 138 is reducedwithout reducing the joint contact length. The points may be eitheracute angle points or obtuse angle points rather than right angle pointsand more or less than the number of points illustrated may be usedwithout departing from the spirit of the invention.

Other embodiments of the offset point middle leg arrangement may beapparent to one skilled in the art after reading the teachings of thisinvention. FIG. 9 illustrates one embodiment where the middle leglamination 148 joins the yoke laminations 150 and 152 with the joints154 and 156, respectively. The joint 154 comprises two mitered portionswhich intersect to form the right angle point 158. The two miteredportions form different angles with the edges of the lamination 148.Various acute angles may be used, such as the 60 and 30 anglesillustrated in FIG. 9. The joint 156 is similarly shaped except that theright angle point 160 is offset from the point 158, that is, one pointis not coincident with a line drawn through the other point and parallelto the longitudinal axis of the lamination 148. Point angles other thanright angles may be used. The magnetic core which is partiallyillustrated in FIG. 9 employs the offset point arrangement and may beconstructed with 2.4 percent less material than the conventionalmagnetic core illustrated in FIG. 2. The decreased penetration of thejoints into the yoke laminations reduces the flux crowding effect andthe core produced isvoidless.

The novel arrangements of the magnetic cores disclosed herein and thosecontemplated by the invention may be employed in stepped-lap typelaminated magnetic cores. Stepped-lap joints substantially improve theperformance of a magnetic core compared to magnetic cores which utilizethe conventional butted-lap type joint. The core loss is lowered, theexciting voltage-ampere requirements are reduced, and the sound level ofthe magnetic core has a lower intensity. In a stepped-lap joint, thejoints between the mitered or diagonal ends of the leg and yokelaminations in each layer of laminations are incrementally offset fromsimilarly located joints in adjacent layers by a predetermined steppedor progressive pattern, with the joints being stepped at least threetimes in one direction before the direction is changed or the pattern isrepeated.

FIG. 10 illustrates an embodiment of the invention wherein a laminatedmagnetic core has stepped-lap joints and a middle leg lamination havingright angle concave and convex points. The core 160 comprises the outerlegs 162 and 164, the middle leg 166, and the yokes 168 and 170. Theouter corner stepped-lap joints 172, 174, 176 and 180 connect the yokelaminations to the outer leg laminations. The geometry of thelaminations which form the middle leg 166 is similar to that of themiddle leg lamination shown in FIG. 3. The middle leg laminations arevertically distributed in a stepped-lap pattern by progressivelynotching one yoke lamination deeper and the other yoke laminationshallower than in the adjacent layer. The middle leg lamination is movedbetween the yoke laminations in the completed core without changing thedimensions of the middle leg lamination. Voids which exist in theyokemiddle leg joints are distributed between the yoke and the middleleg portions of the core.

Various arrangements of step lapping the joints may be used. FIG. 10A,which is a sectional view of FIG. 10 taken at the line X-X, illustratesone arrangement of step lapping the joints. The middle leg laminations182 are butted against the yoke laminations 184, with the butt joints186 incrementally offset from layer-to-layer with four layers oflaminations separating repeating joints in the same plane. Thisarrangement of steppedlap joints is also illustrated in FIGS. 11, 12, 13and 14, however, any other stepped-lap arrangement may be used withoutdeparting from the scope of the invention.

The stepped-lap distribution illustrated in FIG. 10 is achieved byincrementing the joints in a direction parallel to a straight side ofthe middle leg, hence the terminology vertical distribution. Anotherform of vertically distributing the joints is illustrated in FIG. 11.The length of the lamination 188 is changed to progressively step thejoints into the yoke laminations 190 and 192. The convex points 194,196, 198 and 200 are formed by the intersection of the straight portionsof the joints. The angles illustrated are acute, however, obtuse orright angles may also be used.

FIG. 12 illustrates a middle leg arrangement of a laminated magneticcore which is horizontally steppedlapped. The middle leg lamination 202has offset convex points which are shifted horizontally throughout thecore due to the dimensional changes of the middle leg laminations inadjacent layers.

FIG. 13 illustrates a middle leg arrangement of a laminated magneticcore which is angularly steppedlapped, that is, the joints progress in adirection which is between the horizontal and vertical directions. InFIG. 13, the leg lamination 216 butts against the yoke laminations 218and 220 to form the joints 222 and 224. The joints and the offset convexpoints 226 and 228 progress into the yoke laminations 218 and 220 fromlayer-to-layer in an angular fashion. Another angularly distributedstepped-lapped joint arrangement is shown in FIG. 14. Here, the angle ofprogression is more nearly vertical than that shown in FIG. 13. The leglamination 230 connects the yoke laminations 232 and 234 with the joints236 and 238. A line drawn through either of the concave points 240 and242 and its respective points in adjacent layers will indicate thedirection of distribution. In all of the stepped-lap arrangementsdescribed and contemplated herein, laminations may be stacked in groupsand the groups may be stacked with alternate groups reversed. Thisprocedure increases the joint distribution throughout the core.

The laminated magnetic cores described herein offer several performanceimprovements over prior art designs. Tests performed on several of thedifferent embodiments of the invention indicate the superior performanceof the core arrangements disclosed.

A 45 KVA core constructed with the middle leg arrangement shown in FIG.11 and with the outer corner arrangements shown in FIG. was tested andcompared to the standard prior art arrangement shown in FIG. 2. At aninduction level of kilogauss, the true watts per pound loss was improvedby 33 percent, the apparent watts per pound loss was improved by 63percent and the sound level was improved by 3.4 db over the prior artcore. By constructing the core according to this arrangement to providethe same performance as the prior art core, a core steel savings of 9.7percent can be realized along with a conductor material savings of 2percent.

A 45 KVA core constructed with the middle leg arrangement shown in FIG.11, except with four convex points on each end of the middle leglamination, and with the outer corner arrangements shown in FIG. 10, wastested and compared to the standard prior art arrangement shown in FIG.2. At an induction level of 15 kilogauss, the true watts per pound losswas improved by 30 percent, the apparent watts per pound loss wasimproved by 56 percent, and the sound level was improved by 4.0 db overthe prior art core. Core steel savings of 11.5 percent and coppersavings of 2 percent could be realized with this core arrangement.

A 45 KVA core constructed with the middle leg arrangement shown in FIG.14 and with the outer core arrangements shown in FIG. 10 was tested andcompared to the standard prior art arrangement shown in FIG. 2. At aninduction level of i5 kilogauss, the true watts per pound loss wasimproved by 36 percent, the apparent watts per pound was improved by 69percent, and the sound level was improved by 3.4 db over the prior artcore. Core steel savings of 8.3 percent and copper savings of 2 percentcould be realized by using this core arrangement.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all of the matter containedin the foregoing description, or shown in the accompanying drawings,shall be interpreted as illustrative rather than limiting.

We claim as our invention:

1. A laminated magnetic core comprising a plurality of layers oflaminations, said layers stacked with their edges in alignment to definea core having at least three legs and two yokes, each of said layers oflaminations comprising a lamination having two straight sides and firstand second ends, said first end defining a first joint between saidlamination and one of said yokes, said second end defining a secondjoint between said lamination and the other of said yokes, said firstjoint comprising at least one convex point which is formed by theintersection of two straight portions of said first joint, said secondjoint comprising at least one concave point which is formed by theintersection of two straight portions of said second joint, said convexand concave points being equally spaced from the lamination axis whichis parallel to the sides and coincident with the center of thelamination, said first and second joints being distributed with respectto the joints in the other layers, with at least one layer oflaminations separating repeating joints in the same plane.

2. The laminated magnetic core of claim 1 wherein the first joint of thelayer of laminations comprises a plurality of convex points and thesecond joint of the layer of laminations comprises a plurality ofconcave points with the respective convex and concave points beingequally spaced from the lamination axis. 7

3. The laminated magnetic core of claim 1 wherein the concave and convexpoints are formed by straight portions of the joint which intersect toform a right angle.

4. The laminated magnetic core of claim 1 wherein the concave and convexpoints are formed by straight portions of the joint which intersect toform an acute angle.

5. The laminated magnetic core of claim 1 wherein the concave and convexpoints are formed by straight portions of the joint which intersect toform an obtuse angle.

6. The laminated magnetic core of claim 1 wherein the concave and convexpoints are formed by straight portions of the joint which intersect toform a right angle, a first of the straight portions being skew to oneside of the lamination by substantially 30, a second of the straightportions being skew to the other side of the lamination by substantially60.

7. The laminated magnetic core of claim 1 wherein adjacent layers oflaminations are identical and are rotated around an axis to form abutted-lap core with the points of the joints maintaining their spacingfrom the lamination axis.

8. The laminated magnetic core of claim 1 wherein the joints areincrementally offset from layer-to-layer in a predetermined stepped-lappattern with at least two layers of laminations separating repeatingjoints in the same plane.

9. The laminated magnetic core of claim 8 wherein the joints areincrementally offset from layer-to-layer without changing the dimensionsof the middle leg lamination.

10. The laminated magnetic core of claim 8 wherein the predeterminedstepped-lapped pattern progresses only in a horizontal direction.

11. The laminated magnetic core of claim 8 wherein the predeterminedstepped-lapped pattern progresses only in a vertical direction.

12. The laminated magnetic core of claim 8 wherein the predeterminedstepped-lapped pattern progresses only in an angular direction.

13. A laminated magnetic core comprising a plurality of layers oflaminations, said layers stacked with their edges in alignment to definea core having at least three legs and two yokes, each of said layers oflaminations comprising a lamination having two straight sides and firstand second ends, said first end defining a first joint between saidlamination and one of said yokes, said second end defining a secondjoint between said lamination and the other of said yokes, said firstjoint comprising a first convex point which is formed by theintersection of two straight portions of said first joint, said secondjoint comprising a second convex point which is formed by theintersection of two straight portions of said second joint, said firstand second convex points being equally spaced from and on the same sideof the lamination axis which is parallel to the sides and coincidentwith the center of the lamination, said first and second joints beingdistributed with respect to the joints in the other layers with thejoints incrementally offset from layer-to-layer in a predeterminedsteppedlap pattern with at least two layers of laminations separatingrepeating joints in the same plane.

14. The laminated magnetic core of claim 13 wherein the first joint ofthe layers of laminations comprises a plurality of convex points, thesecond joint of the layer of laminations comprises a plurality of convexpoints, with the respective convex points being equally spaced from thelamination axis.

15. The laminated magnetic core of claim 13 wherein the convex pointsare formed by straight portions of the joint which intersect to form aright angle.

16. The laminated magnetic core of claim 13 wherein the convex pointsare formed by straight portions of the joint which intersect to form anacute angle.

17. The laminated magnetic core of claim 13 wherein the convex pointsare formed by straight portions of the joint which intersect to form anobtuse angle.

18. The laminated magnetic core of claim 13 wherein the convex pointsare formed by straight portions of the joint which intersect to form aright angle, a first of the straight portions being skew to one side ofthe lamination by substantially 30, a second of the straight portionsbeing skew to the other side of the lamination by substantially 60.

19. The laminated magnetic core of claim 13 wherein the predeterminedstepped-lap pattern progresses only in a horizontal direction.

20. The laminated magnetic core of claim 13 wherein the predeterminedstepped-lap pattern progresses only in a vertical direction.

21. The laminated magnetic core of claim 13 wherein the predeterminedstepped-lap pattern progresses only in an angular direction.

22. A laminated magnetic core comprising a plurality of layers oflaminations, said layers stacked with their edges in alignment to definea core having at least three legs and two yokes, each of said layers oflaminations comprising a lamination having two straight sides and firstand second ends, said first end defining a first joint between saidlamination and one of said yokes, said second end defining a secondjoint between said lamination and the other of said yokes, said firstjoint comprising a plurality of convex points which are formed by theintersection of straight portions of said first joint, said second jointcomprising a plurality of convex points which are formed by theintersection of straight portions of said second joint, the convexpoints in said first joint which are on one side of the lamination axis,which is parallel to the sides and coincident with the center of thelamination, being spaced from the lamination axis by distances which areunequal to the distances with which respective convex points in saidsecond joint which are on the same side of the lamination axis andspaced therefrom, said first and second joints being distributed withrespect to the joints in the other layers with at least one layer oflaminations separating repeating joints in the same plane.

23. The laminated magnetic core of claim 22 wherein the convex pointsare formed by straight portions of the joint which intersect to form aright angle.

24. The laminated magnetic core of claim 22 wherein the convex pointsare formed by straight portions of the joint which intersect to form anacute angle.

25. The laminated magnetic core of claim 22 wherein the convex pointsare formed by straight portions of the joints which intersect to form anobtuse angle.

26. The laminated magnetic core of claim 22 wherein the convex pointsare formed by straight portions of the joint which intersect to form aright angle, a first of the straight portions being skew to one side ofthe lamination by substantially 30, a second of the straight portionsbeing skew to the other side of the lamination by substantially 60.

27. The laminated magnetic core of claim 22 wherein adjacent layers oflaminations are identical and are rotated around an axis to form abutted-lap core with the points of the joints maintaining their spacingfrom the lamination axis.

28. The laminated magnetic core of claim 22 wherein the joints areincrementally offset from layer-to-layer in a predetermined stepped-lappattern with at least two layers of laminations separating repeatingjoints in the same plane.

29. The laminated magnetic core of claim 28 wherein the predeterminedstepped-lap pattern progresses only in the horizontal direction.

30. The laminated magnetic core of claim 28 wherein the predeterminedstepped-lap pattern progresses only in the vertical direction.

31. The laminated magnetic core of claim 28 wherein the predeterminedstepped-lap pattern progresses only in an angular direction.

i It

1. A laminated magnetic core comprising a plurality of layers oflaminations, said layers stacked with their edges in alignment to definea core having at least three legs and two yokes, each of said layers oflaminations comprising a lamination having two straight sides and firstand second ends, said first end defining a first joint between saidlamination and one of said yokes, said second end defining a secondjoint between said lamination and the other of said yokes, said firstjoint comprising at least one convex point which is formed by theintersection of two straight portions of said first joint, said secondjoint comprising at least one concave point which is formed by theintersection of two straight portions of said second joint, said convexand concave points being equally spaced from the lamination axis whichis parallel to the sides and coincident with the center of thelamination, said first and second joints being distributed with respectto the joints in the other layers, with at least one layer oflaminations separating repeating joints in the same plane.
 2. Thelaminated magnetic core of claim 1 wherein the first joint of the layerof laminations comprises a plurality of convex points and the secondjoint of the layer of laminations comprises a plurality of concavepoints with the respective convex and concave points being equallyspaced from the lamination axis.
 3. The laminated magnetic core of claim1 wherein the concave and convex points are formed by straight portionsof the joint which intersect to form a right angle.
 4. The laminatedmagnetic core of claim 1 wherein the concave and convex points areformed by straight portions of the joint which intersect to form anacute angle.
 5. The laminated magnetic core of claim 1 wherein theconcave and convex points are formed by straight portions of the jointwhich intersect to form an obtuse angle.
 6. The laminated magnetic coreof claim 1 wherein the concave and convex points are formed by straightportions of the joint which intersect to form a right angle, a first ofthe straight portions being skew to one side of the lamination bysubstantially 30*, a second of the straight portions being skew to theother side of the lamination by substantially 60*.
 7. The laminatedmagnetic core of claim 1 wherein adjacent layers of laminations areidentical and are rotated 180* around an axis to form a butted-lap corewith the points of the joints maintaining their spacing from thelamination axis.
 8. The laminated magnetic core of claim 1 wherein thejoints are incrementally offset from layer-to-layer in a predeterminedstepped-lap pattern with at least two layers of laminations separatingrepeating joints in the same plane.
 9. The laminated magnetic core ofclaim 8 wherein the joints are incrementally offset from layer-to-layerwithout changing the dimensions of the middle leg lamination.
 10. Thelaminated magnetic core of claim 8 wherein the predeterminedstepped-lapped pattern progresses only in a horizontal direction. 11.The laminated magnetic core of claim 8 wherein the predeterminedstepped-lapped pattern progresses only in a vertical direction.
 12. Thelaminated magnetic core of claim 8 wherein the predeterminedstepped-lapped pattern progresses only in an angular direction.
 13. Alaminated magnetic core comprising a plurality of layers of laminations,said layers stacked with their edges in alignment to define a corehaving at least three legs and two yokes, each of said layers oflaminations comprising a lamination having two straight sides and firstand second ends, said first end defining a first joint between saidlamination and one of said yokes, said second end defining a secondjoint between said lamination and the other of said yokes, said firstjoint comprising a first convex point which is formed by theintersection of two straight portions of said first joint, said secondjoint comprising a second convex point which is formed by theintersection of two straight portions of said second joint, said firstand second convex points being equally spaced from and on the same sideof the lamination axis which is parallel to the sides and coincidentwith the center of the lamination, said first and second joints beingdistributed with respect to the joints in the other layers with thejoints incrementally offset from layer-to-layer in a predeterminedstepped-lap pattern with at least two layers of laminations separatingrepeating joints in the same plane.
 14. The laminated magnetic core ofclaim 13 wherein the first joint of the layers of laminations comprisesa plurality of convex points, the second joint of the layer oflaminations comprises a plurality of convex points, with the respectiveconvex points being equally spaced from the lamination axis.
 15. Thelaminated magnetic core of claim 13 wherein the convex points are formedby straight portions of the joint which intersect to form a right angle.16. The laminated magnetic core of claim 13 wherein the convex pointsare formed by straight portions of the joint which intersect to form anacute angle.
 17. The laminated magnetic core of claim 13 wherein theconvex points are formed by straight portions of the joint whichintersect to form an obtuse angle.
 18. The laminated magnetic core ofclaim 13 wherein the convex points are formed by straight portions ofthe joint which intersect to form a right angle, a first of the straightportions being skew to one side of the lamination by substantially 30*,a second of the straight portions being skew to the other side of thelamination by substantially 60*.
 19. The laminated magnetic core ofclaim 13 wherein the predetermined stepped-lap pattern progresses onlyin a horizontal direction.
 20. The laminated magnetic core of claim 13wherein the predetermined stepped-lap pattern progresses only in avertical direction.
 21. The laminated magnetic core of claim 13 whereinthe predetermined stepped-lap pattern progresses only in an angulardirection.
 22. A laminated magnetic core comprising a plurality oflayers of laminations, said layers stacked with their edges in alignmentto define a core having at least three legs and two yokes, each of saidlayers of laminations comprising a lamination having two straight sidesand first and second ends, said first end defining a first joint betweensaid lamination and one of said yokes, said second end defining a secondjoint between said lamination and the other of said yokes, said firstjoint comprising a plurality of convex points which are formed by theintersection of straight portions of said first joint, said second jointcomprising a plurality of convex points which are formed by theintersection of straight portions of Said second joint, the convexpoints in said first joint which are on one side of the lamination axis,which is parallel to the sides and coincident with the center of thelamination, being spaced from the lamination axis by distances which areunequal to the distances with which respective convex points in saidsecond joint which are on the same side of the lamination axis andspaced therefrom, said first and second joints being distributed withrespect to the joints in the other layers with at least one layer oflaminations separating repeating joints in the same plane.
 23. Thelaminated magnetic core of claim 22 wherein the convex points are formedby straight portions of the joint which intersect to form a right angle.24. The laminated magnetic core of claim 22 wherein the convex pointsare formed by straight portions of the joint which intersect to form anacute angle.
 25. The laminated magnetic core of claim 22 wherein theconvex points are formed by straight portions of the joints whichintersect to form an obtuse angle.
 26. The laminated magnetic core ofclaim 22 wherein the convex points are formed by straight portions ofthe joint which intersect to form a right angle, a first of the straightportions being skew to one side of the lamination by substantially 30*,a second of the straight portions being skew to the other side of thelamination by substantially 60*.
 27. The laminated magnetic core ofclaim 22 wherein adjacent layers of laminations are identical and arerotated 180* around an axis to form a butted-lap core with the points ofthe joints maintaining their spacing from the lamination axis.
 28. Thelaminated magnetic core of claim 22 wherein the joints are incrementallyoffset from layer-to-layer in a predetermined stepped-lap pattern withat least two layers of laminations separating repeating joints in thesame plane.
 29. The laminated magnetic core of claim 28 wherein thepredetermined stepped-lap pattern progresses only in the horizontaldirection.
 30. The laminated magnetic core of claim 28 wherein thepredetermined stepped-lap pattern progresses only in the verticaldirection.
 31. The laminated magnetic core of claim 28 wherein thepredetermined stepped-lap pattern progresses only in an angulardirection.